Preparation And High Temperature Properties Of CeO₂ Modified Co-based Spinel Coating By Electrodeposition

Solid oxide fuel cell（SOFC）have attracted much attention because of their high energy efficiency,low pollution and high fuel adaptability.As one of the important components of SOFC,the interconnect plays an important role in blocking the cathode and anode atmosphere and conducting the current.Compared with other materials,ferritic stainless steel is widely used because of its good electrical and thermal conductivity,low manufacturing cost and other advantages.However,the element of Cr in ferritic stainless steel diffuses outward to form a Cr oxide layer resulting in increased resistance,while causing cathode"Cr poisoning".At present,the main method to solve the above problem is to prepare high-temperature antioxidant coating on the surface of ferritic stainless steel connection body.Compared with other types of coatings,spinel coatings are of great interest because of their high conductivity and excellent ability to inhibit Cr diffusion.The Ni-based spinel coating with poor electrical conductivity and the Cu-based spinel coating with poor oxidation resistance are not effective in protecting the joints,while the Co-based spinel coating with good oxidation resistance and thermal stability is favored,but it still faces many problems such as thickening of the Cr-containing oxide layer and decreasing electrical conductivity during long-term service.It was found that doping of CeO₂ in spinel coatings can slow down the diffusion of Cr elements and improve the bonding force between the coating and the interconnect,thus improving the high temperature oxidation resistance and electrical conductivity of the interconnect.Based on the above analysis,the Co-based spinel coating modified by CeO₂ was prepared by electrodeposition,and the effects of the process parameters and the modification amount of CeO₂ on the microstructure of Co-based spinel coating were studied systematically,its high-temperature oxidation resistance and electrical conductivity is also discussed,and the mechanism of the effect of CeO₂ on the high-temperature performance of Co-based spinel coating is elucidated.The main research conclusions are as follows:（1）By adjusting the electrodeposition duty cycle to 40%,the deposition temperature to50°C and the electrolyte p H to 4,a flat,dense and uniform grain size Co₃O₄ spinel coating with a thickness of about 16μm can be prepared on the surface of SUS430 substrate,which is tightly bonded to the substrate.The Co₃O₄ spinel coating was doped with appropriate amount of CeO₂to refine the grains,but the content of CeO₂ was too high to inhibit the crystallization of the grains,and the optimal modification amount of CeO₂ was finally determined to be 6 g/L.The phase composition of Co₃O₄ and its modified coating did not change after oxidation at 800°C for 168 h.Compared with the Co₃O₄ spinel coating,the thickness of the Cr-containing oxide layer was significantly smaller after oxidation of its modified coating.（2）By adjusting the electrodeposition duty cycle to 60%,the deposition temperature to40°C and the electrolyte p H to 3,a Co-Fe-Ni spinel coating with a thickness of about 7μm and a dense and uniform surface was successfully prepared on the surface of SUS430 substrate,whose main phases were（Co,Fe,Ni）₃O₄ and Co₃O₄ spinel phases.Co-Fe-Ni and its modified coating still maintain a dense and small thickness of Cr oxide layer after long time oxidation.（3）The results of the high-temperature oxidation resistance and electrical conductivity tests showed that the doping of CeO₂ in the Co-based spinel coating could effectively enhance the oxidation resistance and electrical conductivity of the coating.Among them,the oxidation rate constant(2.0095×10^-14 g²·cm^-4·s^-1)and surface specific resistance（14.6 mΩ?cm²）of the CeO₂-modified Co-Fe-Ni spinel coating are lower than those of Co-Fe-Ni spinel and Co₃O₄ and their modified coatings,which have the best high-temperature oxidation resistance and electrical conductivity.